Understanding the Layers of a Roof and How Many Are Typical

A roof is made up of several layers, each serving a specific purpose. The typical number of layers can vary depending on the type of roof and its design.

A standard residential roof usually has three main layers: the underlayment, the roofing felt, and the shingles. The underlayment is a layer of waterproof material that protects the roof from moisture.

The roofing felt is a layer of asphalt-saturated paper that provides additional protection against weathering and wear. This layer is usually applied over the underlayment.

A typical residential roof can have up to five layers, including the roof deck, the underlayment, the roofing felt, the shingles, and the ridge cap.

In most states, you're only allowed to have 2 layers of shingles on a roof for fire safety reasons.

The maximum number of layers allowed on a roof depends on the type of roofing material used, with asphalt shingles, cedar shakes, and rubber shingles topping out at 2 layers, while metal roofs or concrete roofs usually stop at 1 layer.

A roof deck, also known as sheathing, is the layer installed over the framing and provides the base for the shingles, with common materials including plywood or OSB sheets.

Underlayment, a protective layer installed onto the roof deck, offers an extra layer of water resistance against leakage caused by ice dams, and is usually felt, a durable paper saturated with asphalt.

The roof's underlayment prevents rain from infiltrating under the shingles and also prevents water from reaching the roof deck should the shingles be torn or broken.

The roof deck is the layer installed over the framing and provides the base on which everything else is laid. It's the foundation of your roofing system.

Most homes have plywood or OSB sheets as the material used for decking. Other materials like corrugated metal, reinforced concrete, polystyrene, and double tee are also used.

The roof deck provides a nail bed for the shingles. This is crucial for securing the shingles and keeping them in place.

A roof deck can be made of various materials, but plywood and OSB sheets are the most common choices.

Underlayment is a protective layer installed onto the roof deck. It's usually made of felt, a durable paper saturated with asphalt.

This extra layer provides an additional line of defense against water damage. It's especially important because it's the last line of defense if water gets to the decking.

Roof underlayment is installed directly over the decking and provides an extra layer of protection from the elements. This includes rain and ice dams that can cause leakage and damage.

The most common types of roof underlayment are felt, 15 lb felt, 30 lb felt, or synthetic. Each type offers its own level of water resistance and durability.

Having the right underlayment can make a big difference in preventing water damage to your roof. It's a crucial step in maintaining the integrity of your roof and preventing costly repairs.

The top layer of your roof system is the one you see from the street, and it's what most people think of when talking about a roof. This layer will be the type of roofing material you choose, such as asphalt shingles, metal roofing, cedar shake roofing, or synthetic roofing.

Asphalt shingles are a popular choice, but if you're unsure what type of roof fits your needs, there's a Roof Type Quiz that can help you find the right roofing material.

This layer will make up the bulk of your roof, and it's the one that's most visible to the public eye.

You can have up to 2 layers of shingles on a roof for fire safety reasons, but you'll often see more than that due to the cost of replacement.

Most roofs won't be a good candidate for a nail-over reroof, which can be done if the situation is right.

A nail-over reroof requires an asphalt roof that's near the end of its lifespan, with shingles lying down flat and no lifted or cracked shingles.

You'll also need a roof with only a few penetrations, a small amount of flashing, and no walls butting up against the shingles.

The type of roofing material used affects the number of layers allowed, with asphalt shingles, cedar shakes, and rubber shingles maxing out at 2 layers.

Metal roofs and concrete roofs usually stop at 1 layer.

You can have up to 2 layers of shingles on a roof for fire safety reasons. Most states only allow this to ensure the roof doesn't become a fire hazard.

If you already have 2 or more layers, a contractor will likely recommend a full replacement. This is because multiple layers can weigh down the roof and cause structural issues.

A nail-over reroof is possible if the current roof has only one layer of shingles. However, this option is usually only considered if the roof is near the end of its lifespan and is in good condition.

Asphalt roofs must have only a few penetrations, a small amount of flashing, and no walls that butt up against the shingles to be a good candidate for a nail-over. Ultimately, it's up to the contractor's inspection to determine if this is an option.

The maximum number of layers for asphalt shingles, cedar shakes, or rubber shingles is 2. This is the same for metal roofs and concrete roofs, which usually only have one layer.